Field of the Invention
The present invention relates to an image processing apparatus and a control method thereof, and relates to a technique for performing user assistance of a follow shot by an image capturing apparatus.
Description of the Related Art
A follow shot exists as a photographic technique for expressing a sense of speed of an object (moving body). This photographic technique is intended for stopping a moving object image and following a background image by performing panning of a camera with the movement of the object by a photographer. In a typical follow shot, an exposure time is adjusted so as to be longer than that in a normal time with a moving speed of the object. Japanese Patent Laid-Open No. 2010-245774 discloses a configuration for performing photographing in an exposure time so as to sufficiently secure a follow amount of the background during the follow shot.
If a panning velocity is not appropriate when the photographer performs panning with the movement of the object in the follow shot, a difference occurs between the moving speed of the object and the panning velocity, whereby the object images are often blurred. To solve the inconvenience, there has been proposed a method of absorbing the difference between the moving speed of the object and the panning velocity by the movement of a shift lens (hereinafter referred to as “follow shot assistance”), which serves as a technique for assisting the follow shot by a user. Japanese Patent Laid-Open No. 2006-317848 disclose discloses an apparatus that detects the object based on a blur detection by a gyro sensor and a motion vector of the image and calculates a correction amount for positioning the detected object at a center of the image. An optical axis is corrected by the movement of the shift lens and the follow shot is performed.
In the correction by using the shift lens disclosed in Japanese Patent Laid-Open No. 2006-317848, a maximum angle where a system can correct (hereinafter referred to as “maximum correctable angle”) is limited because the movable range of the shift lens is limited. Therefore, a situation in which the system cannot correct may occur. Hereinafter, a specific description will be given by assuming a situation shown in FIG. 9.
FIG. 9 illustrates the speed of the object and the panning velocity of the camera, each of which is shown by angular velocities centering on the principal points. The angular velocity of the object is at 30 deg/sec and the panning angular velocity of the camera is at 24 deg/sec in degrees. In this case, a camera system needs to assist 6 deg/sec, which is the difference between both of the angular velocities. A value multiplying the angular velocity assisted by the system by the exposure time becomes a correction angle by which the system will finally need to assist. As one example, a photographing in which the maximum correctable angle of the shift lens is 0.4 degrees and the exposure time is 1/16 seconds is assumed. The correction angle finally needed is below.
                              6          ×                      1            16                          =                  0.375          ⁢                                          ⁢                      (                          ≤              0.4                        )                                              [                  Formula          ⁢                                          ⁢          1                ]            
In this example, the correction angle is the maximum correctable angle or below, and thus, the correction is possible.
In contrast, when photographing in which the exposure time is ⅛ seconds is performed, the correction angle finally needed is below.
                              6          ×                      1            8                          =                  0.75          ⁢                                          ⁢                      (                          >              0.4                        )                                              [                  Formula          ⁢                                          ⁢          2                ]            
In this example, the correction angle exceeds the maximum correctable angle, and thus, the correction becomes impossible. The follow shot needs a long exposure time and the correction angle exceeds the maximum correctable angle, and thus, the correction may be impossible.